// 1像素边框处理
border-1px($color)
  position :relative
  &:after
    display :block
    position :absolute
    left :0
    bottom :0
    width :100%
    border-top :1px solid $color
    content :' '

border-none()
  &:after
    display :none

// 处理2x 3x图片  
bg-image($url)
  background-image :url($url+"@2x.png")
  @media(-webkit-min-device-pixel-ratio:3),(min-device-pixel-ratio:3)
    background-image :url($url+"@3x.png")